Improve document structure and organization.

[jasonjgw]

• Restructure and clarify discussion of meeting platform development and selection in section 3.
• Consolidate the two subsections on meeting platform selection into section 3.
• Section 6 was actually guidance for meeting hosts that belongs in section 5.1. Move the guidance into section 5.1 and delete section 6. Make editorial changes to the material moved into section 5.1.
• Clarify heading.
• Clarify scope of section.